function getRem(pwidth,prem){
	var html=document.getElementsByTagName("html")[0];
	var oWidth=document.body.clientWidth||document.documentElement.clientWidth;
	html.style.fontSize=oWidth/pwidth*prem+"px";
}
window.onload=function(){
	getRem(640,100);
}
window.onresize=function(){
	getRem(640,100);
}